Blowout is one of the most serious accidents in the drilling process of hydrogen sulfide (H 2 S) oil and gas wells, often accompanied by the leakage of H 2 S and other toxic gases, which easily causes casualties and huge economic and environmental losses. Therefore, this article uses DEMATEL and ISM hybrid algorithms to establish a blowout accident-causing network model for oil and gas wells with H 2 S content, thus strengthening the risk management. In this model, firstly, the general causative factors of blowout accidents are extracted by accident statistics. Secondly, expert knowledge is adopted to determine the correlation matrix among factors. Thirdly, based on the DEMATEL algorithm, the degree of the relationship among the factors is analyzed. The importance degree (centrality) of each factor and its status as well as role (causality) in the accident-causing system are given. Finally, the ISM algorithm is used to classify the factors and establish an accident-causing network diagram with hierarchical relationship. The proposed model has been applied in a gas field containing H 2 S in East Sichuan, China. The results show that causative factors of blowout accidents can be divided into cause group and effect group according to the influence relationship among them. The cause group implies the meaning of the causative factors, and the effect group denotes the meaning of the causative factors. Hence, it would be necessary to control and pay great attention to the cause group factors beforehand. The key causative factors of blowout accidents are geological exploration technology, safety monitoring facilities and on-site safety culture, which belong to the cause group and are at the basic level of the accident-causing network diagram. This model has provided effective decision-making guidance for HSE work in gas field and reduced the incidence of blowout accidents. This model uses a combination of qualitative and quantitative methods to analyze the causes of blowout accidents, not only considering the relationships between factors and accidents, but also considering the relationships between factors and factors. As a result, it provides decision-making basis for the prevention and control of blowout accidents in H 2 S oil and gas wells.

Abstract Both in Europe and in North America, the goal to use increasing amounts of renewable energy has created the need for electricity storage. One concept which aims to address this need is to produce hydrogen from surplus electricity, and to use the existing natural gas pipeline system to transport and store said hydrogen. Generally, the hydrogen content in the pipeline flow would be below 20%, thus avoiding the problems of transporting and burning pure hydrogen. The thermodynamic properties of hydrogen-natural gas mixtures, as well as their impact on the combustion process are briefly addressed. To assess the impact of hydrogen addition in various concentrations to a natural gas pipeline, a realistic pipeline system is simulated. The pipeline hydraulic simulation provides the necessary operating conditions for the gas compressors and the gas turbines that drive these compressors. The impact on transportation efficiency in terms of energy consumption as well as the impact on the transport capacity of a pipeline where the equipment was sized originally for natural gas transport, are assessed. Introduction and Background The increased use of renewable energy will require the capability to store energy to balance the large fluctuations in the availability of renewable energy, thus balancing supply and demand. Generating green Hydrogen from surplus electricity using electrolysis and transporting this hydrogen together with natural gas in gas pipelines is a method to provide storage and transportation for hydrogen [1,2,3]. Mixing hydrogen into natural gas pipelines requires a number of considerations regarding the compression of this mixture, the use of the mixture as a fuel for the gas turbines that drive the pipeline compressors, and the impact of pipeline capacity and transport efficiency. There are a number of other concerns, including safety concerns for gas compressor packages, and material issues related to hydrogen embrittlement on rotating parts like impellers, pressure containing vessels (like compressor bodies), and high-pressure pipes. [4].

Abstract This paper elaborates on a method previously reported that characterized a materials susceptibility to hydrogen embrittlement in a seawater environment under CP by monitoring the crack growth rate of ASTM (1) E1820 1 pre-cracked CT specimens at various constant stress intensity (K-levels) and at varying cathodic protection potentials. For the fastener grade ASTM A320 L7 & L43 2 grade carbon alloy material the initial reported results showed that the material susceptibility to hydrogen embrittlement followed a pattern influenced by the yield strength level of the material, specifically that material susceptibility is distinguished by the response to varying CP potential & applied K levels. Intermediate yield strength (< 930 MPa) for example, showed multiple K 1EAC threshold responses; while known susceptible material with very high strength levels showed reduced threshold response and insensitivity to more positive CP potentials. The paper presents additional results from those previously reported covering the yield strength levels between 725 MPa (105ksi) and 964 MPa (140ksi) and highlighting the transition between non-susceptibility to susceptibility right about 939 MPa (135ksi) and close to the hardness limit of HRC 34 identified in API 2 20e 3 . These results can be represented graphically and can serve to establish design operating limits for the materials in a seawater environment under CP. Characterizing Hydrogen Embrittlement Susceptibility – Methodology Overview Materials properties that are used in specific oil and gas environments are de-rated due to the risks associated with hydrogen embrittlement cracking. In oil production environments the concern is for the onset of stress corrosion cracking (SCC), while in seawater environments the concern is for Hydrogen Induced Stress Cracking (HISC). Both are hydrogen embrittlement phenomena with the distinction being the source of hydrogen for each. In SSC the source of hydrogen is from the presence of H 2 S in the oil production fluids, and in HISC the source of hydrogen is from the dissociation of water from the cathodic protection system. This paper is focused on the latter phenomena and aims to characterize the susceptibility of carbon alloy steels as applied in fastener applications, in a seawater environment under cathodic protection.

Abstract Microstructure and strength affect hydrogen embrittlement (HE) susceptibility of martensitic steels. In order to understand their respective roles, two martensitic steels with the same chemical composition, but different strength (and or hardness) levels were selected. Incremental step load (ISL) technique was used to evaluate the environmental hydrogen embrittlement susceptibilities (EHE) of the materials by in-situ charging of hydrogen at a cathodic potential of −1.2V SCE . Microstructural characterization was performed using TEM. Stress and hydrogen concentration distributions at the time of failure were estimated from a stress coupled hydrogen diffusion finite element analysis (FEA). It was primarily observed that microstructure controlling strength has a more significant effect on HE failure, as compared to microstructure affecting hydrogen diffusion in case of EHE. This observation was further corroborated with fractographic analyses and qualitative discussion based on linear elastic fracture mechanics (LEFM). Introduction Quench and tempered (Q & T) martensitic steels are widely used to manufacture fasteners. These frames, bridges and other structural components. However, premature failures of these fastener components due to hydrogen embrittlement (HE) can lead to total loss of structural integrity and catastrophic failures. For instance, the HE cracking of high strength anchor rods and structural bolts in the San Francisco–Oakland Bay Bridge is a notable incident. 1 However, HE in martensitic steels is a complex phenomenon and has been a topic of research for decades. 2,3 The identification of the factors responsible for HE, involves fundamental considerations implicating the entire fastener supply chain, starting from the steel mill, the fastener manufacturer, the coater, all the way to the end user. The selection of heat treatment process could be considered as a decisive factor towards the prevention of HE failure of threaded fasteners. In general, fastener specifications place broad restrictions on material selection, without any mandate on the selection of a particular grade of steel. As a result, it is necessary to develop a better understanding on the susceptibility of these materials to HE. Based on the sources of hydrogen ingress into the steel structure, there are two broad categories of HE: a) internal hydrogen embrittlement (IHE) which is a delayed failure, caused by residual hydrogen from steelmaking, surface cleaning, electroplating in particular. 4,5 And, b) environmental hydrogen embrittlement (EHE), which occurs due to the introduction of hydrogen by sacrificial corrosion during service such as subsea applications. It is also generally accepted that strength (and or hardness) have a first-order effect on HE susceptibility in high-strength martensitic steels, with an increase in hardness and/or yield strength leading to a decrease in resistance to HE failures. 6–8 However, the underlying mechanism(s) that make strength a significant factor in influencing HE susceptibility needs further understanding.

Abstract Precipitation-hardened nickel alloys (PHNAs), such as UNS N07718, are commonly used in oil and gas subsea service for components such as bolts, fasteners and gaskets, which require high strength and corrosion resistance. Numerous subsea failures of these materials have been attributed to hydrogen embrittlement (HE) caused by hydrogen evolved by cathodic protection (CP) systems, and in the presence of geometrical design features, i.e. grooves, notches, threads etc. acting as stress raisers, and sometimes a compromised microstructure associated with inappropriately controlled alloy manufacturing processes. Although the coexistence of a susceptible microstructure, sufficiently high stress and hydrogen content is deemed necessary for cracking to occur, the significance of those parameters and their complex interrelationship is not understood. The lack of such understanding calls into question the relevance of the widely-used test methodologies for designing and assessing with PHNAs, as it is not established what combination of parameters is of highest significance to be monitored and measured. In previous work, the co-authors and other researchers have extensively used slow strain rate tensile (SSRT) testing of plain-sided (un-notched) specimens, primarily as a qualitative screening method, to rank the HE resistance of various alloys in different microstructural conditions. In some cases, attempts have been made to use the test and its results to obtain a quantitative insight into the cracking sequences and stress/strain thresholds. Whilst the majority of the test outputs have inherently been qualitative, observations of slip bands on the brittle fracture surfaces of SSRT test specimens suggest the mechanism of HE is associated with a degree of plastic strain and strain localization prior to crack initiation. Given the significance of such a strain threshold, and the observation that most failures occur at stress concentrators, this study explores the role of stress raisers on the resistance of UNS N07718 to HE, using notches with different stress concentration factors (SCFs) introduced into the test specimens. SSRT testing and incremental step load (ISL) testing were combined with finite element (FE) modelling to investigate the usefulness of each approach in terms of providing a robust, quantitative assessment and design criterion for HE resistance, based on a hypothesized threshold of critical strain localization to activate HE crack initiation in PHNAs.

Abstract Precipitation-hardened nickel alloys (PHNAs) are widely used for demanding oil and gas subsea applications, because of their high strength and corrosion resistance. However, several failures were associated with hydrogen embrittlement, under cathodic protection (CP), as subsea CP systems can provide a source of atomic hydrogen, which can diffuse into the material and compromise its toughness. The risk of hydrogen embrittlement might be reduced if CP systems were appropriately designed, e.g. more positive CP potentials could locally be applied to CRA components. Whilst tailored CP profiles will remain a practical challenge, the relationship between the CP potential and localised loading, due to the presence of stress raisers, is yet to be established. This paper aims to address whether there is a threshold potential, above which embrittlement will not occur, and whether this threshold will be a function of stress intensity/concentration factor. This was explored through conducting slow strain rate tensile (SSRT) and incremental step load (ISL) testing on UNS (1) N07716, which has previously been associated with failures, at potentials between -750 and -1050mV Ag/AgCl , on plain-sided specimens. Additional fracture-toughness-based testing, using single edge notch bend (SENB) specimens, was undertaken to understand if the stress intensity (associated with a fatigue pre-crack), can increase susceptibility to embrittlement. Introduction Precipitation hardened nickel alloys are commonly used in demanding and aggressive environments where a combination of high strength and corrosion resistance is required. They are therefore frequently selected for applications requiring high strength in downhole, wellhead, subsea and Christmas tree applications 1 . The microstructure of all PHNAs consist of a primary austenitic (Y) phase, which is solid solution strengthened by alloying elements, such as Cr, Mo and Ti. UNS N07716, includes additions of Nb and Ti and is therefore also strengthened by Y' (Ni 3 Al/Ti) and Y" (Ni 3 Nb) precipitates, which are dispersed through the matrix 2 . The microstructure of PHNAs can also include the non-strengthening and deleterious δ and laves phases, and various metal carbides.

Abstract Hydrogen embrittlement susceptibility of precipitation hardened Ni- alloys is a complex function of several factors such as chemical composition, deformation mode, grain size and grain boundary precipitation of carbides and intermetallic phases. Understanding the role of these factors is fundamental in identifying metallurgical conditions that can enhance resistance of precipitation hardened Ni-alloys to hydrogen embrittlement. Analysis of hydrogen embrittlement data and a new test program have been carried out to further investigate the role of such factors and determine metallurgical conditions capable of improving hydrogen embrittlement resistance of UNS N09955 and UNS N07716 alloys. Results of the study are presented and discussed in this paper. Introduction Precipitation hardened (PH) Ni-alloys are widely used in the oil and gas industry since they provide an excellent combination of corrosion resistance and mechanical strength. Their use in the manufacture of API 1 6A pressure-containing and pressure-controlling components is subject to the stringent requirements of specification API Standard 6ACRA. (1,2) However, matching the requirements of API Standard 6ACRA does not preclude susceptibility of some PH Ni-alloys to hydrogen embrittlement (HE) and this in some cases has led to premature and unexpected failures of components made from such materials. (3-5) Much effort has been devoted to understanding HE. Several mathematical models have been proposed to describe the complex interaction between hydrogen and material microstructure in terms of several factors, i.e. deformation mode, chemical composition, grain size and grain boundary precipitation of carbides and intermetallic phases. (6-11) Understanding the role of these factors is fundamental in identifying metallurgical conditions that can enhance HE resistance of PH Ni-alloys. In this paper, analysis of HE data and a new test program have been carried out to further investigate the role of such factors and determine metallurgical conditions that are helpful in improving HE resistance of UNS N09955 and UNS N07716 alloys. Results of the study are presented and discussed in this paper. For brevity, in the following text alloy UNS N09955 is identified as alloy 955 and alloy UNS N07716 is identified as alloy 716.

Abstract After a number of failures in the Oil and Gas industry research works on hydrogen embrittlement (HE) of nickel-based alloys has been quite significant. Much work had been done previously in other industries, nuclear and aeronautic in particular. Despite this work, a lot remains to be understood. Among them, precipitation-hardened (PH) nickel alloys UNS N07718 has been significantly studied and its HE resistance is now better assessed based on its microstructure. Less work has been performed on some of the other PH nickel alloys, although, their HE resistance is better appreciated from recent literature data. The results published at NACE Corrosion 2019 from a large JIP study indicated that PH nickel alloys could be split in three families with less susceptible alloys, like UNS N07718, UNS N09925 and UNS N09935, more susceptible alloys like UNS N07725 and UNS N07716, while alloy UNS N09945 had variable susceptibility. Besides PH nickel alloys, other solution-annealed or cold worked alloys are used in environments where hydrogen can be present. As PH alloys they are also susceptible to HE, but published studies are scarce. This paper is a review of internal and published work setting the base of our current understanding on the HE resistance of various PH, solution annealed and cold worked nickel-based alloys. Consequences on the use of these alloys are discussed for Oil and Gas applications. Introduction A literature survey and results of internal studies have been used to summarize our knowledge concerning hydrogen embrittlement (HE), also called HSC (hydrogen stress cracking) or HISC (hydrogen-induced stress cracking) of nickel-based alloys, specifically alloys in use in the upstream Oil and Gas industry. Since the first major failure reported in an HPHT well in early 2000's a number of studies have completed previous work primarily on UNS (1) N07718 in the nuclear and aeronautics and space industries. Other alloys have since been developed specifically for the upstream Oil and Gas production, while others were already in use. The objective of these alloys is to be resistant to internal corrosion in severe sour conditions, where carbon and low alloy steels cannot be used, and be also resistant to HSC in case hydrogen charging occurs in wells and subsea components. This means these alloys must be listed in NACE (2) MR0175/ISO 15156 Standard with high sour limits and they should have the highest possible resistance to HSC. This paper only deals with HSC and attempts to give an update on the current knowledge on the resistance of nickel-based alloys to HSC and how they can be used in the field to avoid failures.

Abstract Sacrificial aluminum-indium anode cathodic protection is commonly used for protecting offshore and subsea structures. As a consequence, all metallic fasteners are hydrogen charged under high tensile stresses at the thread roots. This means that material selection must prevent the occurrence of hydrogen stress cracking (HSC) under these conditions. For most equipment where low strength fasteners are sufficient a low alloy steel can be used provided a maximum yield strength and hardness are specified. When higher strength fasteners are required, low alloy steels must be replaced by corrosion resistant alloys which must be qualified with regard to their susceptibility to HSC. In this work, precipitation-hardened nickel alloys from API 6ACRA, work hardened austenitic stainless steels and nickel alloys with yield strengths up to 200 ksi (1240 MPa) have been tested under cathodic protection using a specific test methodology. The objective was to quantify their resistance to HSC and identify their limits of use when exposed to cathodic protection. The results are presented and discussed in the light of current knowledge on HSC for subsea fastener applications. Introduction Bolted connections for subsea flanges and other components must be reliable as they are often used for pressure containing components (subsea Christmas trees, connectors …). When possible, the primary choice for bolting is low-alloy steel with a limitation of actual yield strength (135 ksi) and a maximum hardness of 34 HRC to prevent HSC. In some cases, the use of low-alloy steel is prohibited and corrosion resistant alloys (CRAs) must be used. This is the case when higher strength is required and also for sour service resistance under thermal insulation. In addition, CRAs do not require temporary corrosion protection coatings. There is limited literature dealing with high strength subsea fasteners. Eskalul et al. listed possible alloys for use as subsea fasteners with yield strength above 150 ksi. Among these they highlighted alloys with good resistance to environment-assisted cracking (EAC) including some martensitic stainless steels (SS), precipitation-hardened (PH) nickel alloys and cobalt alloys. 1,2

Abstract In this study the hydrogen diffusion and trapping characteristics of four API line pipe grade steels were investigated during electrochemical charging. In addition, the slow strain rate (SSRT) method was used to determine the steels resistance to hydrogen embrittlement in terms of ductility ratio and time to failure. Permeation tests were used to characterise the hydrogen diffusivity and apparent solubility, whilst complimentary thermal desorption tests were used to assess the hydrogen solubility and to characterise the nature of the trapped hydrogen. From the results obtained, it was shown that irreversibly trapped hydrogen was present in all steels in the absence of hydrogen charging (as-received state). Furthermore, hydrogen introduced during electrochemical charging was reversible in nature for all steels. Comparison of hydrogen embrittlement resistance with the determined diffusion and trapping characteristics revealed improved performance for steels with lower diffusivity and higher hydrogen solubility. The trend with diffusivity was explained in terms of a critical hydrogen concentration for failure, which was shown to be higher in steels with lower diffusivity. This critical concentration was reached much later in the steels with lower diffusivities, thus giving improved ductility ratios and longer failure times in the SSRT tests. Introduction In line pipe steels exposed to sour service conditions and under stress, hydrogen atoms may be generated on the exposed pipe surface. Over time, this hydrogen can diffuse into the metal bulk, leading to reduced ductility and increased susceptibility to cracking. This is known as hydrogen embrittlement. 1 Apart from sour service, hydrogen embrittlement in linepipe may also arise from the use of cathodic protection systems. 2 Considering the above processes, the bulk diffusion of hydrogen in the steel is expected to influence a pipelines resistance to embrittlement. Furthermore, hydrogen diffusion is strongly influenced by the microstructure i.e. trapping. Generally, hydrogen may be bound strongly to some trap sites e.g. fine incoherent precipitates, and dislocation cores, which are then known as irreversible traps. 3,4 On the other hand hydrogen may also interact more weakly with other microstructural features (reversible traps), e.g. dislocation strain fields and semi-coherent precipitates. 3 In terms of hydrogen embrittlement resistance, characterisation of the hydrogen diffusion coefficient, as well as the concentration of trapped hydrogen and its nature, i.e. reversibly or irreversibly trapped, may help to rationalise different line pipe steels performance.

Abstract Centrifugal tubes resistant to high temperatures, whose nominal composition is 25 Cr, 35 Ni, 1 to 1.5 Nb, 0.4 C, Fe balance, have been examined both from a mechanical/metallurgic point of view and a design one in relation to the construction of furnaces to produce hydrogen by catalytic reforming (temperature 850 to 950°C and circumferential stress 10 to 15 MPa for approximately 11 years, i.e. 100,000 hours). An assessment of the Fitness for Purpose that considers the characteristics of the material as supplied might overestimate in a non-conservative way the material reliability. Therefore, based on a vast collection of results obtained with this type of material, the data acquired were gathered in a single method, which can be used as a practical tool for Fitness for Purpose evaluations and to proper schedule maintenance and inspections. Specifically, three different states of degradation of the tube material have been identified: as cast (new material, as supplied by the manufacturer), slightly degraded and moderately degraded. The mechanical properties at ambient temperature (hardness and upper yield point), the microstructure and creep resistance have been considered, on the whole, to define Larson-Miller stress-parameter curves for each of the above conditions. The method obtained allows for a reliable assessment of the residual life and more accurate planning of inspections and/or replacements of tubes showing greater degradation, considering the most appropriate resistance curve (intended as the relationship between acting stress and the Larson-Miller parameter) for the actual conditions of the material, identified on tubes in operation with diametral measurements, hardness tests, metallographic replicas or, if possible, fast non-time-dependent destructive tests (e.g. micrographs). Introduction Centrifugal tubes in Fe-Ni-Cr alloy (nominal composition 25 Cr, 35 Ni, 1-1.5 Nb, 0.4 C and Fe balance) are used, among other applications, in the chemical and petrochemical industry to produce hydrogen by steam reforming. Suitable catalysts and a temperature between 850 and 950°C are required to obtain steam reforming reaction. The tubes, typically arranged vertically and filled with the catalysts, are heated up to their operating temperature with gas burners (Figure 1).

Abstract Alloy A975, a super austenitic stainless steel in the cold worked condition has been commonly used in drilling applications, where its combination of composition and high strength makes it highly resistant to pitting corrosion and fatigue. Now, after 15 years of use in drilling, this material can be considered for other oilfield applications. Three commercial heats of cold worked (CW) A975 were subjected to different tests to assess its resistance to environmental assisted cracking. For reference, slow strain rate tests (SSRT) were performed at NACE MR0175 Levels VI and VII. Additionally, C-ring tests per NACE TM0177 Method C were performed at NACE MR0175 Levels V and VI to support the SSRT results. Light optical microscopy and scanning electron microscopy were used to analyze the specimens before and after the tests. The SSRT show good ductility values compared to reference tests up to NACE Level VI. The C-ring testing also indicates similar cracking resistance under these conditions. The results from SSRT under cathodic potential also demonstrate good resistance against hydrogen embrittlement. Introduction Industries use super austenitic stainless steels (SASS) to withstand pitting and crevice corrosion in both acidic and neutral environments containing high chlorides. SASS and austenitic stainless steels are commonly categorized by their contents of Cr, Mo, and N, as represented by the pitting resistance equivalent number (PREN). Although different definitions of PREN exist, for this study the NACE MR0175/ISO 15156 definition was utilized (F PREN = W Cr + 3.3(w Mo + 0.5W W ) + 16W N ). 1 When PREN exceeds 40, the prefix ‘super’ is colloquially added to these types of stainless steel (e.g., super duplex stainless steel). A975 in the cold worked (CW) condition has been used for more than 15 years as a material for nonmagnetic drill collars where high pitting corrosion resistance and fatigue resistance are needed. These tools typically require heavy wall thicknesses to apply maximum weight to the drill bit, and a special cold forging process is used to achieve high strength throughout the cross section. The ability to achieve high strength is aided by the composition, and alloys for nonmagnetic applications typically contain Mn and N, which facilitate this by dramatically increasing the rate of work hardening. Other oilfield tools need high strength in heavy sections, for example, certain downhole safety valve and packer components. For applications of these tools in sour fluids, precipitation hardening (PH) Ni alloys are traditionally used. However, there have been recent accounts of hydrogen embrittlement with some PH Ni alloys, which has occurred from hydrogen charging or ingress from a variety of sources. 2-4 Therefore, there is an opportunity for alternative, high strength corrosion resistant alloys if it can be shown they are suitably resistant to these effects. This study presents new results for CW A975 from sour service tests [i.e., slow strain rate tests (SSRT) and C-Ring tests] and hydrogen embrittlement (HE) tests. The aim of this study is to demonstrate acceptable performance of CW A975 for use under hydrogen charging and in severe sour conditions (NACE Level VI for Type 4c) according to Tables A.12 and A.14 in NACE MR0175/ISO15156:2015.

Abstract There is a growing network of hydrogen pipelines operating in the United States: 1,600 miles (2,575 km) are already in place. Throughout their lifecycle, hydrogen gas pipeline assets need to be inspected periodically for safety and integrity of supply. Magnetic flux leakage (MFL) has been used for decades as an in-line inspection (ILI) technology. Because MFL tools must be durable and robust, their design has relied on well-established materials such as high strength alloy steels and rare earth permanent magnets. These materials are especially susceptible to hydrogen embrittlement, which occurs when a material is mechanically stressed while being exposed to hydrogen. Successfully inspecting hydrogen-carrying pipelines while reducing the risk of hydrogen embrittlement requires the use of alternate materials and methods to develop a capable ILI tool. This white paper will discuss the challenges of this unique inspection environment, which were resolved through innovative ILI tool design and focused pipeline operation during the inspection process. Introduction Air Products, which manufactures and sells chemicals and gases for industrial use, operates the world's largest hydrogen pipeline network, the Gulf Coast Connection Pipeline (GCCP). GCCP runs 183 miles (295 km) between Plaquemine, Louisiana, and Port Neches, Texas, uniting 22 hydrogen plants and creating a network consisting of 600 miles (966 km) of pipe. [2] The GCCP is an 18-inch pipeline with bi-directional flow capabilities which give Air Products the ability to transport hydrogen safely to where the demand is highest and keep the refineries and plants along the Texas Gulf Coast operating at full capacity. Heavy wall thickness pipe was selected for all above-ground sections to protect against damage from vehicle impacts. Construction began in May 2011 and was completed in August 2012. In the United States, hydrogen transportation by pipeline falls under Code of Federal regulations (CFR) 49, Department of Transportation (DOT) 192 regulations that require verification of pipeline integrity. This can be accomplished through a number of methods, including pressure test, in-line inspection (ILI) and direct assessment. The GCCP pipeline passes through DOT high consequence areas (HCA) for approximately 1.26% of the total pipeline length.

Abstract The hydrogen embrittlement susceptibility of several UNS N07718 microstructures was determined with different in situ testing techniques. Hydrogen-affected stress intensity factors for crack initiation and for unstable crack growth were determined through incremental step load (ISL) and rising displacement (RD) testing coupled with the direct current potential difference (DCPD) method. Slow strain rate (SSR) tensile tests were also performed to evaluate hydrogen embrittlement susceptibility. Microstructures with no δ phase and three different strength levels and a microstructure with an intermediate strength level that contained δ phase were evaluated. For UNS N07718 microstructures without δ phase, the stress intensity factor for unstable crack growth increased with increasing yield strength and exhibited an inverse relationship with the total elongation ratio from the SSR tests. The presence of δ phase decreased the stress intensity factor for unstable crack growth but did not affect the stress intensity for crack initiation. Fracture modes were evaluated with scanning electron microscopy and were independent of testing method. Introduction UNS( 1 ) N07718, commonly referred to as alloy 718, is one of several precipitation-hardened nickel-base corrosion resistant alloys (CRAs) used for components in deep sea oil wells. Ni-base CRAs are used for packers, tubing hangers, fasteners, valves, and bolting components in deep-sea oil wells because of their high-strength, high toughness, and corrosion resistance; however, field failures of these components have occurred due to hydrogen embrittlement. 1-3 Precipitation-hardened Ni-base CRAs are primarily strengthened by coherent and/or semi-coherent Y" and Y' precipitates formed during aging. Thermomechanical processing and aging may also result in the formation of additional precipitates at grain boundaries, such as δ phase, and carbides within grains. It is well known that δ phase can increase the hydrogen embrittlement susceptibility of Ni-base CRAs by inducing hydrogen-affected intergranular and/or interphase cracking. 1, 2 , 4-6 API( 2 ) standard 6ACRA provides guidelines for annealing and aging heat treatments and acceptable mechanical properties of UNS N07718 and other Ni-base CRAs for use in downhole environments. 7 In certain service conditions, UNS N07718 can experience hydrogen embrittlement despite being heat treated according to the API 6ACRA standard due at least in part to limited δ-phase precipitation along grain boundaries, 2 3 these precipitates are formed during the aging step of the heat treatment. The effect of the Y" and Y' precipitates on hydrogen embrittlement in Ni-base CRAs when δ phase is not present is unclear, in part due to the difficulty of producing high strength microstructures with no δ phase.

Abstract A preliminary analysis of failed prestressing strands within a post-tensioned tendon on the Wando River bridge in South Carolina showed signs of possible hydrogen embrittlement. One proposed source of hydrogen is through galvanic coupling that may exist between the galvanized steel duct and the steel strands. This coupling, if present, can promote hydrogen evolution at the steel strand's surface which may or may not be mitigated by the condition and quality of the grout. To fully understand the susceptibility of post-tensioned steel strands to hydrogen embrittlement in galvanized steel tendon ducts, the conditions that promote hydrogen production, the kinetics of hydrogen evolution and adsorption into the steel, as well as the subsequent loss of strength need to be well understood. In an effort to avoid these costly failures in the future, the likely effects of grout quality and the presence of grout deficiencies within galvanized steel ducts will be deduced from prior knowledge of hydrogen embrittlement mechanisms of cold-drawn steels. The focus of the review will be placed on studies and reports that have detailed the kinetics of hydrogen production and adsorption on cold drawn steel strands, and the relationship between stress state and hydrogen content distribution on strength reduction. Introduction Cold-drawn pearlitic steel wire is used to form reinforcing strands in pre and post-tensioned reinforced concrete structures. One particular application of this material is the strands within post-tensioned (PT) bridge tendons. The tendons consist of multiple 7-wire strands contained within a High-density Polyethylene (HDPE) or rigid steel duct. The tendons run continuously through the center of multiple spans of the bridge making contact with spans through concrete deviator blocks which help form the profile of the tendon. Within the concrete deviator blocks and pier segments, the duct is a more rigid material such as galvanized steel. The ends of the tendon are anchored down at bulkheads and stressed after which the duct is filled with cementitious grout [1]. The alkaline grout is intended to provide protection against corrosion but, due to voids in the grout and/or areas of improper mixing, cases of severe corrosion have occurred.

Abstract Electrochemical impedance spectroscopy (EIS) is a powerful technique that can detect and provide information about different phenomena that occur on the corroding surface using alternating current signals. Several electrochemical reactions and associated phenomena, such as mass transfer and chemical reactions happening at and near the metal surface, occur simultaneously. Therefore, the EIS data conducted at a specific DC potential often contain mixed information about several of those reactions, while at other potentials the EIS data are dominated by a single electrochemical reaction. To be able to focus on a single electrochemical reaction and its associated phenomena, it is important to identify the DC potential at which the EIS data provide the most relevant information about this reaction, otherwise, the analysis of the impedance data becomes very difficult. This work aims to show an example of how to select the DC potential range at which the hydrogen evolution reaction is dominant. Following this step, the EIS data can be used to determine the diffusion coefficient of hydrogen ion in a strong acid aqueous solution. Introduction EIS is a powerful tool, yet a challenging technique for studying of a corrosion electrochemical system. It can provide a broad range of information by decoupling the phenomena that occur at or near the metal surface 1-5 . In the study of corrosion of mild steel in a strong acid solution, the main electrochemical reactions are anodic dissolution of iron and the cathodic reduction of hydrogen ions and water (at lower potentials). In EIS studies of these electrochemical reactions, choosing the appropriate DC potential is of great importance. For example, to study the hydrogen reduction reaction, which is often controlled by the mass transfer of hydrogen ions, a DC potential must be chosen at which the EIS response provides mostly information about the hydrogen reduction reaction and the influence of other reactions on measured impedance is minimized. It is well known that at potentials below the open circuit potential (OCP), the measured current is dominated by hydrogen ion reduction. We are compelled to conclude that the impedance at these same potentials below the OCP is also dominated by the hydrogen reduction reaction? But, is this always the case?

Abstract The objective of this research is to obtain a quantitative description of the effect of adsorbed H 2 S and chloride on the hydrogen penetration in high strength low alloy (HSLA) carbon steel, by evaluating the response of hydrogen permeation current and the formation of characteristic inductive response using hydrogen permeation and electrochemical Impedance spectroscopy methods on HSLA carbon steel C110. The hydrogen permeation flux measured in Devanathan-Stachurski cell suggests that enhance effect of H 2 S on absorption of hydrogen following an adsorption isotherm behavior as a function of the H 2 S activity in solution. The inductive response of electrochemical impedance spectroscopy (EIS) showed consistency with effect of adsorption of H 2 S. The EIS results also indicate that the coverage of H 2 S was suppressed by chloride. A good correlation about the effect of adsorbed chloride was found between inductive response and hydrogen permeation flux. Introduction HSLA steels play an important role in oil and gas storage and transportation, where H 2 S and water exist in 1-4 . However, the application of HSLA steel is limited by corrosion and mechanical problems exposure to wet H 2 S environment, e.g., HIC and sulfide stress cracking (SSC) 5 . A recent study 6 shows that, by adjusting the brine ionic strength, it is possible to obtain different values of the threshold stress intensity parameter K ISSC at the same concentration of dissolved H 2 S or H 2 S fugacity. It was suggested that the explanation for that behavior is due to the relationship between the K ISSC and the subsurface hydrogen concentration which is heavily dependent on the coverage of the metal surface by absorbed H 2 S as indicated by Cancio et al 7,8 . The relevant aspect is that at constant brine strength and pH the H 2 S coverage on the steel surface is controlled by the H 2 S activity. The interaction between the H 2 S contained within the corrosive environment and the low alloy steel interface is the subject of many studies in the literature 9-11 , the consensus indicates that a layer of adsorbed H 2 S or containing sulfides is formed depending the H 2 S concentration and the solution pH 12-14 . The role of the adsorbed layer of H 2 S or sulfide appears to be critical to understand the hydrogen permeation behavior in HSLA steels which show that the apparent diffusion coefficient that reflects the effect of the sulfide layer, affects to the susceptibility for SSC cracking 15 . The results from literature propose that the role of H 2 S in promoting hydrogen uptake in the steel occurs either by suppressing the hydrogen recombination reaction at metal surface, or by catalyzing hydrogen absorption through the presence of the sulfide layer. 16,17 The relationship between this factors and the C 0 can be expressed in the following way: 18 (equation)

Abstract The present work explores permeation testing of specimens which are simultaneously loaded in tension to investigate hydrogen-assisted cracking. In this experimental technique, the global hydrogen flux and the mechanical loading are continuously monitored during a tensile test of specimens with U- and V-notches at various cathodic polarization current densities. These experimental conditions allow assessment of the susceptibility of steels under various intensities of hydrogen flux and concentration in several mechanical states. Diffusible hydrogen led to quasi-cleavage fracture at the hydrogen entry surfaces for all the tested conditions. The results of the permeation test (under tensile loading) are incorporated into finite element modeling (FEM) for the evaluation of local conditions for the development of quasi-cleavage fracture, as well as the sensitivity of these threshold conditions (stress, plastic strain, hydrogen flux and concentration) to the intensity of the applied cathodic polarization. Introduction The present work addressed the challenge of developing higher-strength low-alloy martensitic steels for sour service which are resistant to hydrogen-assisted cracking by evaluating a test method in which a permeation test is performed on a specimen which is simultaneously subjected to an applied tensile load. The design of this experimental technique consists of an electrochemical permeation Devanathan-Stachurski cell built on a 100 kN tensile machine, which allows continuous monitoring of the global hydrogen flux and mechanical loading during the tensile test of prismatic notched and unnotched specimens until fracture. Hydrogen changes considerably the fracture mechanisms of martensitic steels. Intergranular and quasi-cleavage hydrogen-induced fracture surfaces are often observed in the presence of hydrogen instead of ductile morphology of air-tested specimens. 1-3 Despite the numerous studies on hydrogen embrittlement of martensitic steels, 1-8 it is still not clear how hydrogen promotes quasi-cleavage fracture and the role of plasticity in this process. Recent studies have shown that the damage is a result of a combined effect of local hydrogen concentration, hydrogen flux, hydrostatic stress and plastic strain. 7,8 This paper continues these investigations and increases comprehension of the local threshold conditions (hydrogen flux and concentration, mechanical state), which are necessary for the appearance and development of hydrogen-assisted quasi-cleavage fracture in martensitic steels.

Abstract Alloy UNS N07718 (known as Alloy 718) is a precipitation hardening nickel alloy containing additions of chromium, niobium, titanium, aluminum and molybdenum. This combination of elements provides an alloy with a combination of high yield strength and corrosion resistance required in sour service applications. Through the precipitation hardening heat treatment, the alloy precipitates the intermetallic Gamma Prime (ordered fcc Ni 3 Al) and Gamma Double Prime (bcc tetragonal Ni 3 Nb) phases, which are responsible for elevating the yield strength of the material. Additionally to the importance of these both phases in the hardening process, previous studies showed that the microstructure of Alloy 718 may also have a direct influence on its susceptibility to Hydrogen Embrittlement. Laboratory melts with modified compositions based on Alloy UNS N07718 were produced and tested to correlate both mechanical and hydrogen embrittlement properties. The testing plan included mechanical testing, Slow Strain Rate Tensile (SSRT) tests under cathodic protection and numerical thermodynamic simulations. Introduction Its outstanding mechanical performance and its very good corrosion resistance have turned Alloy UNS N07718 into the most preferred applied nickel alloys in the Oil & Gas industry. 1 However, recent field component failures reported the occurrence of hydrogen embrittlement, 2 which can be a serious limitation to the material application. The continuing development of oil and gas production industry pushes the needs to develop new materials technology for applications involving high temperatures, high pressures and increasingly aggressive service environments. 3 The outstanding mechanical features of Alloy UNS N07718 are resultant of the precipitation of the intermetallic phases Gamma Prime (ordered fcc Ni 3 Al) and Gamma Double Prime (bcc tetragonal Ni 3 Nb), which is allowed by the presence of the alloying elements niobium, aluminum and titanium. Previous studies show that the strengthening phases Gamma Prime and Gamma Double Prime play an important role on the corrosion resistance of the alloy UNS N07718. 4-10 Gosheva et al. have made important contributions clarifying the impact of microstructure on the hydrogen embrittlement susceptibility of UNS N07718. 8 Their studies concluded that the amount of hydrogen stored in the material during cathodic hydrogen charging was predominantly dependent on the strengthening precipitates and their interface with the Gamma matrix. The precipitates act as trapping sites, slowing down the diffusion process. Klapper et al. showed that the amount and size of precipitates such as Gamma Prime and Gamma Double Prime, as well as the Delta phase, rather than the strength or hardness level only, predominantly affected the hydrogen embrittlement susceptibility and defined the type of embrittlement mechanism. 9 According to his studies, HEDE- (Hydrogen Enhanced Decohesion) and HELP (Hydrogen Enhanced Localized Plasticity)-assisted shear localization may occur on oil-patch N07718 depending on the amount and localization of Delta phase.

Abstract Low Alloy steels (LASs) are, by volume, the most widely used alloy family in critical oil & gas (O&G) components. However, the strength and hardness of LASs for sour environments are limited to prevent different forms of hydrogen embrittlement, such as hydrogen stress cracking (HSC) and sulfide stress cracking (SSC). Moreover, ISO 15156-2 (1) restricts LASs to a maximum of 1 wt% Ni due to SSC concerns. In the present work, the hydrogen diffusivity of the nuclear-grade ASTM(2) A508 Gr.4N LAS was measured using the hydrogen permeation method. Results are linked to quenched and tempered (Q&T) microstructure features characterized by transmission electron microscopy (TEM). Additionally, a comparison was made between the A508 Gr.4N and a ferritic-pearlitic steel with similar Ni content. This work is connected with the HSC evaluation of the same alloy by slow strain rate testing (SSRT) described in a separate publication. Material requirements for unconventional Oil and Gas environments Due to the progressive depletion of conventional oil and gas (O&G) reserves, the energy demand drifts its attention to unconventional reservoirs. 1 These new O&G fields pose challenges to the materials used that are often associated with high-pressure (>103 MPa) and high temperature (>177 °C) or, in arctic service, temperatures as low as -60°C. 1-3 Moreover, the presence of atomic hydrogen produced either from corrosion reactions or by cathodic protection can lead to hydrogen stress cracking (HSC). In sour environments, the cracking mechanism is referred to as sulfide stress cracking (SSC) in which H 2 S acts as a hydrogen recombination poison and increases severity. Materials susceptible to hydrogen embrittlement (HE)—by either HSC or SSC—characterized by ductile behavior under normal circumstances, can fracture in a brittle mode in the presence of atomic hydrogen. Therefore, materials selection is paramount to reduce possible catastrophic failures. Use of high strength low alloy steels for sour service applications Low alloy steels (LASs) are widely used because of their low cost and good mechanical properties. 1 By appropriate heat treatment processing, a high yield strength (e.g., 690 MPa (100 ksi)) can be achieved while retaining adequate toughness. The hardenability can be enhanced by the addition of alloying elements such as molybdenum, chromium, and nickel. 4 Nickel additions produce an increase in yield strength (YS) due to solid solution strengthening and subgrain size reduction. 1, 5 Hardenability is improved with Ni as it stabilizes the austenite phase, delaying the austenite to martensite transformation. 1 Additionally, Ni increases the low-temperature fracture toughness due to grain refinement and modification of the ferrite properties. 6 Furthermore, Ni has a low impact on weldability as reflected by its carbon equivalent coefficient, which is the lowest compared with other alloying elements. 1